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Accelerating the Newton MessagePad 120

WARNING: THIS IS NOT AN END-USER DOCUMENT. This document describes a hardware modification which is neither endorsed nor authorized by Apple Computer, Inc. and which will void all warranties pertaining to the affected product. Carrying out the procedure described below requires an advanced level of technical skill and experience working on surface-mount equipment. This document is provided for informational purposes only and the author expressly disclaims any responsibility for direct, incidental, consequential, special or other juridically recognized category of damages sustained as a result of carrying out the procedures described herein or otherwise making use of the information.

This document is © Copyright 1998 by Lewin A.R.W. Edwards. You may reproduce it freely provided you do not modify it in any way. The author may be reached as sysadm@zws.com, or via his WWW server, http://www.zws.com/.

Abstract

The MessagePad 120 runs at a standard clock speed of 20MHz. It is possible to accelerate this speed by replacing the oscmod from which the CPU clock is derived with a faster module. Most MessagePad 120s should work at 25MHz; faster speeds may be possible. However, as this modification involves running parts outside their specifications, it is impossible to state precisely what range of speeds is available.

The CPU clock in the MP120 is derived from a 40MHz oscmod located on the underside of the main logic PCBA.

Side-Effects

  1. Battery life will be reduced slightly by this modification.
  2. Although the procedure is reversible, it involves applying heat to delicate components. For this reason it is not recommended to experiment too many times with different speeds.

Procedure

  • Ensure that you have the following tools and parts: Temperature controlled soldering iron with fine point, desoldering tool, small Philips-head jewelers' screwdriver, 50MHz 4-pin surface-mount oscmod.
  • Back up all data on your MessagePad.
  • Remove the screen cover, battery compartment cover and main battery from your MessagePad and lay the unit screen-side-down on a soft surface (e.g. a mouse mat).
  • Remove the eight screws indicated by red squares in Fig.1 below.

MP120 rear view
Fig.1 Screws securing MP120 rear casing.

  • Starting at the serial/DC input port, gently prise the top portion of the casing off with your fingers, taking care not to break the plastic claws which hold it on.
  • Remove the five screws indicated by red squares in Fig. 2 below.

MP120 interior view 1
Fig.2 Screws securing logic PCBA to interior of MP120.

  • Desolder the two 2-conductor film connectors indicated by red circles in Fig. 3 below, and the 4-conductor ribbon cable indicated by a red rectangle. Also disconnect the LCD feed, indicated by a heavy blue rectangle - ensure that you release the cable grip by sliding the locking bar out (to the left as held in this photograph). NB: The film connector which leads to the DC input/serial subassembly is covered by a piece of insulating tape (shown in the photograph). Retain this piece of tape and replace it during reassembly. CAUTION: Take extreme care not to overheat the film connectors or stress them unduly - for example, do NOT bend them through sharp angles. Also note that the 4-conductor ribbon cable has no polarity markings; it is advisable to mark the PCB and the cable with a spirit pen before desoldering it.

MP120 interior view 2
Fig. 3 Cables which must be desoldered to remove MP120 logic PCBA.

  • You can now remove the main logic PCBA by lifting gently. Note that it is still tethered to the screen side of the MessagePad by two wires. It is not necessary to desolder these wires, as they have sufficient slack to allow the logic PCBA to be turned through 180° and laid alongside the screen section of the unit.
  • You now have access to the CPU side of the logic PCBA. The location of the factory-fitted 40MHz oscmod is indicated in Fig. 4 below. Desolder this component and replace it with a 50MHz oscmod.

MP120 PCBA view
Fig. 4 Location of CPU clock module on MP120 main logic PCBA.

  • Follow the disassembly steps above in reverse. Before replacing the back cover, verify that the two 2-conductor film connectors have been resoldered, the 4-conductor ribbon cable has been resoldered in the correct orientation, and the LCD feed has been reconnected and secured with the connector's locking bar. Also ensure that the plastic power switch actuator and rubber reset button are correctly installed.
  • Your MessagePad should now be running at 25MHz. Restore your data from the backup you made above, if necessary.


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